They are busy ( ) a research ( ) environment A to,

发布时间：2021-03-08 06:36:50

They are busy ( ) a research ( ) environment A to,on B on,at C with,on D with,at 选哪个 为什么

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选C.be busy with sth忙于某事,on sth 关于...
======以下答案可供参考======
供参考答案1:
选C with ， on
be busy with 忙于某事
on envitonment 关于环境
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